1. Technical Field
The present invention relates to the field of construction of underground projects, specifically to an inverse construction method for a deep, large and long pit assembling structure of a suspension-type envelope enclosure.
2. Description of Related Art
At present, ternary-structure geological features, similar to Wuhan grade I soil, includes an upper part which is a fine-grained sediment layer of flood land phase, a lower part which is a coarse-grained sediment layer of riverbed phase, and a bottom layer which is a rock-formation geological structure. The traditional basement construction requires that the designed depth of pit enclosure walls reaches the rock formation, which generates a huge cost. Aiming at the construction of underground enclosure structures at alluvious soft layers along rivers and seas and at geological structures with relatively high underground water levels, the following approaches are usually employed to achieve a water-blocking effect and to prevent surrounding soil layers from sedimenting because of water pumping. 1. The anti-seeping curtain extends to the rock formation or other clay waterproof layer, and other support structures such as grouting piles are provided in front of the curtain in accordance with the design requirements. 2. The anti-seeping curtain and the support structures form the integrated cast-in-place underground continuous wall, and the wall extends to the rock formation or waterproof layer also serves as a waterproof and anti-seeping support structure. 3. The soil body is excavated by layers and the internal supports are constructed layer by layer. Such design has the advantage that the anti-seeping runs through the underground continuous wall of the whole soft soil layer, capable of effectively preventing the underground water from bursting into the basement.
However, such construction mode has the following defects: 1. the continuous wall has a large depth, so the construction cost is high, and on the basis of meeting the requirements for preventing bumping at the pit bottom and ensuring stability, the underground continuous wall has a depth which is more than 2-4 times the marking depth; 2. the cast-in-place wall has a relatively large depth, and due to difficulties in control over the verticality and in assurance of the casting quality of large-depth grooves, weak joints are formed between adjacent pieces of the underground continuous walls, which causes potential hazards of water leak and seepage, results in collapse of the surrounding ground and threatens the pit stability. 3. As the scale of the underground project becomes larger and the pit construction time increases, the “time-space effect” is bad for protection of the environment around the pit. 4. Due to an extremely low ratio of the reinforced area of a passive zone to the pit area, the reinforcement of the soil body of the passive zone fails to play a full role of stabilizing the pit. 5. The lateral wall of a fully closed water-proof curtain on the lateral wall of the riverside low-terrace pit bears a large water pressure, and when affected by the geological conditions of the terrace binary structure characteristics, tends to generate seepage or pipe gush which results in excessive sedimentation in surroundings and cause collapse in serious cases to endanger the pit stability. 6. The traditional inverse construction method has low soil excavation efficiency and greatly affects the pit construction efficiency, while the sequence construction method consumes a large amount of templates in the links of dismantling horizontal supports, replacing supports and laying basement floor-slabs and causes huge labor, material and financial expenses to the project.